[clang] [analyzer] Check the correct first and last elements in cstring.UninitializedRead (PR #95408)

[Kristóf Umann via cfe-commits]

Szelethus wrote:

I merget the PR as is, but I'll keep the warning message in mind, I'm open to changing it as we are getting closer to moving out-of-alpha.

https://github.com/llvm/llvm-project/pull/95408